This invention relates to a disc driving device for rotating an information recording disc such as a magnetic disc.
The disc driving device for rotating the information recording disc such as a magnetic disc is known in Japanese Utility Model Laid-open No. 58-30965, for example.
FIG. 1 is a vertical sectional view of a conventional magnetic disc driving device as described in Japanese Utility Model Laid-open No. 58-30965. Referring to FIG. 1, a base 1 comprises a substrate 1a and a cylindrical retaining portion 1b integrally formed with the substrate 1a. An annular stator 2 is mounted on the outer circumference of the retaining portion 1b. Two bearings 3 are fitted to the inner circumference at upper and lower ends of the retaining portion 1b. Reference numeral 4 designates a pre-pressure spring. A rotation shaft 5 is rotatably supported through the bearings 3 to the retaining portion 1b. A cylindrical hub 6 is so provided as to surround the retaining portion 1b, and is comprised of a top wall 6b fixed to the upper end of the rotating shaft 5 and a flange 6a formed at the lower end of the hub 6. A rotor magnet 7 is mounted through a rotor yoke 8 to the inside wall of the hub 7 in opposed relation with the stator 2. The rotor magnet 7 and the stator 2 form a driving means M for applying a rotational force to the hub 6. A plurality of information recording discs 9 are mounted to the outer circumference of the hub 6, and are layered on the flange 6a with plural spacers 10 interposed therebetween. A cap 11 is fixedly mounted on the top wall 6b of the hub 6 to fix the magnetic discs 9 together with the spacers 10. A magnetic shield plate 12 is provided on the base 1 so as to reduce influence of undue magnetic leakage from the rotor magnet 7, etc. to the outside of the device.
In operation, when a field of the rotor magnet 7 is detected by a magnetism sensing device (not shown) for example to detect a position of the rotor magnet 7, and current to the stator 2 is changed according to the position of the rotor magnet 7, the hub 6 fixed to the shaft 5 supported through the bearings 3 to the base 1 is rotated by utilizing an electromagnetic force between the rotor magnet 7 and the stator 2 to thereby rotate the magnetic discs 9 fixed to the hub 6. Further, magnetic leakage from the rotor magnet 7, etc. to the outside of the device is reduced by the magnetic shield plate 12.
However, in the disc driving device of this type, since information recording/reproducing accuracy is remarkably reduced due to slight play of the rotating shaft, a high dimensional accuracy at the engaged portion between the bearings 3 and the base 1 is severely required. To this end, the base 1 is made of well workable materials such as aluminum. However, since aluminum or the like has a relatively small strength in contrast with a good workability, a bearing portion of the base 1 is apt to be flexed or inclined due to inbalance at the rotating portion. As a result, vibration of the rotating shaft 5 is increased to reduce the information recording/reproducing accuracy. Furthermore, in order to suppress such flexing or inclination of the bearing portion as greatly as possible, thickness of the base 1 cannot be so reduced, and therefore it is difficult to make the device compact.